SUBSTITUENT EFFECTS ON REACTIVITY OF ARYNES . PRODUCT DISTRIBUTIONS AS AN INDEX OF RELATIVE REACTIVITIES OF ARYNES IN METHYLAMINE AND DIMETHYLAMINE SOLVENTS

The competition between the anion of acetonitrile and methyl- or dimethylamine for various substituted arynes has been studied. The product distribution, per cent amine/per cent nitrile, was found to increase in all cases as the substituent was varied along a series, H, CH3, OCH3, Cl, and F, with a more marked increase in the product distribution being observed for 3-arynes than for 4-arynes. In addition, a linear free-energy relationship has been found between the log (% amine/% nitrile)G/(% amine/% nitrile)H, where the subscripts G and H represent the substituted and unsubstituted benzyne intermediates, respectively, and the absolute value of the polar substituent constant,σ′. Therefore, it is concluded that both +I and -I substituents destabilize arynes by inductively polarizing the “triple bond” of benzyne. © 1969, American Chemical Society. All rights reserved.